Resistance spot welding is widely used in industry. In the automotive industry, the ultimate strength performance of resistance spot welds is a critical factor in design, particularly as a result of the need for vehicle weight reduction and downgaging of sheet metals (downgaging affects the strength of a resistance spot weld). What is needed is a quick and effective means for determining the ultimate strength capacity of spot welds under different stress conditions, to enable engineers to determine the number of resistance spot welds needed or to check if the resistance spot welds would fail under given loading conditions.
At the present time, welded joints can be tested in tensile shear by a machine which grasps the ends of two welded test strips and pulls in opposite directions in a plane parallel to the test strips. However, a welded joint is often subjected to loads not only in shear but also perpendicular to the plane of the welded sheet metal as well as intermediate acute angles. The fixture of the present invention is designed to test the load strength of welded sheet metal strips perpendicular to the plates and also at selected intermediate acute angles.
More specifically, the fixture of this invention is designed to test the strength of a resistance spot weld connecting two overlapping test strips, the fixture comprising two identical test units each having a clamping frame for gripping one of the test strips. Pull bars are mounted on the clamping frames of the two test units in alignment with one another and in selected angular positions. A separating force is applied to the strips by a pulling mechanism attached to the pull bars. The pulling mechanism, while not part of the invention, has a means for measuring the amount of force required to cause a weld failure and thus determine the strength of the welded joint. Since the pull bars can be mounted in various different angular positions, including one position perpendicular to the test strips, it is possible to test the strength of the resistance spot weld for stress in any of several different directions to assist an engineer in determining the strength of the weld under many conditions and the number of resistance spot welds needed in a particular application.
One object of this invention is to provide a fixture for testing the strength of resistance spot welds having the foregoing features and capabilities.
Another object is to provide a test fixture which is composed of a relatively few simple parts, is rugged and durable in use, and is capable of being inexpensively manufactured and easily and quickly operated.
These and other objects, features and advantages of the invention will become more apparent as the following description proceeds, especially when considered with the accompanying drawings.